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    SubjectRe: [PATCH v3 0/6] Composefs: an opportunistically sharing verified image filesystem
    On Mon, Feb 6, 2023 at 9:32 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
    >
    > On Mon, 6 Feb 2023 at 18:16, Amir Goldstein <amir73il@gmail.com> wrote:
    >
    > > it's not overlay{erofs+erofs}
    > > it's overlay{erofs+ext4} (or another fs-verity [1] supporting fs)
    > > the lower layer is a mutable fs with /objects/ dir containing
    > > the blobs.
    > >
    > > The way to ensure the integrity of erofs is to setup dm-verity at
    > > erofs mount time.
    > >
    > > The way to ensure the integrity of the blobs is to store an fs-verity
    > > signature of each blob file in trusted.overlay.verify xattr on the
    > > metacopy and for overlayfs to enable fsverity on the blob file before
    > > allowing access to the lowerdata.
    > >
    > > At least this is my understanding of the security model.
    >
    > So this should work out of the box, right?
    >

    Mostly. IIUC, overlayfs just needs to verify the signature on
    open to fulfill the chain of trust, see cfs_open_file():
    https://lore.kernel.org/linux-fsdevel/9b799ec7e403ba814e7bc097b1e8bd5f7662d596.1674227308.git.alexl@redhat.com/

    Thanks,
    Amir.

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